Cathode ray tube graticule



July 30, 1968 L. s. YAGGY CATHODE RAY TUBE GRATICULE Filed Dec. 2, 1966United States Patent 3,395,305 CATHODE RAY TUBE GRATICULE Leou S. Yaggy,North Carlsbad, Calif., assignor to Hughes Aircraft Company, CulverCity, Calif., a corporation of California Filed Dec. 2, 1966, Ser. No.598,849 1 Claim. (Cl. 313-92) ABSTRACT OF THE DISCLOSURE In providing avisible graticule for use in visual analysis of a cathode ray tubedisplay, the present invention structurally incorporates an electricallyconductive layer on the internal surface of the tube viewing screen andprovides a phosphor pattern thereon of determined configuration whichincludes voids effecting a visible display of the desired graticuleduring tube operation. The invention is particularly advantageous in lowcontrast tubes wherein the provision of an effective visible graticulehas heretofore been difiicult to provide. Additionally, the density ofthe phosphor layer may be improved as compared to prior art tubes ofthis type in that the patterns provided offer escape paths for secondaryelectrons to collect at the conductive layer. Thus storage and writingspeed characteristics may be improved.

The invention relates to cathode ray tubes, generally, and hasparticular utility in that type of tube, which, because of operationalmode, has inherent low-contrast characteristics. For example, bistabletubes are illustrative of tubes having inherent low contrastcharacteristics. The invention, therefore, provides a novel tubestructure with a visible graticule and additionally aids in theoperation of the tube.

Cathode ray tubes are frequently used for visual wave display patternsand other time and amplitude-varying phenomena. In the examination ofsuch visual displays, it is sometimes desirable to provide a visiblegraticule to aid in the visual analysis of the display. Graticulesgenerally comprise a network of perpendicularly arranged lines spaced ina predetermined relationship to each other to give visual effect toaspects of the phenomena being reviewed.

In my application Ser. No. 492,800, filed Oct. 4, 1965, Patent No.3,356,881, I described a mode of manufacturing and providing anilluminated graticule for certain cathode ray tubes. The inventiontherein disclosed resulted in an illuminated internal graticule whichhad no effect on the contrast of a stored display. In certainlowcontrast tubes, such as bistable storage tubes, the techniquedescribed in the earlier-filed application is not particularlyadvantageous because of the inherent lowcontrast characteristics of suchtubes. Additionally, the meshless bistable storage tube requires acombination viewing screen and illuminescent storage surface directlyexposed to the electron beam, hence, the invention of my earlier-filedapplication cannot generally be applied thereto.

The operating principle of meshless bistable storage tubes generallyrequires a transparent conductive layer positioned on the glass viewingscreen. A phosphor coating then covers the conductive layer to provideboth luminescence and an ability to accept a charge for elapsed timeimage viewing. The transparent conductive layer usually acts as acollector electrode for secondary electrons which escape the storagelayer during tube operation. In order to accommodate such secondaryelectron collection, it has heretofore been the practice to provide anextremely low-density, or sparse phosphor layer which, in effect, offersinnumerable voids in its surface per- 3,395,305 Patented July 30, 1968mitting the secondary electrons to pass therethrough and be captured bythe exposed transparent conductive coating. A disadvantage of thispractice is that the low-density phosphor is not conducive to providinga sharp and clear display. Additionally, writing speed is importantlyreduced.

In an effort to provide an internal graticule visible during tubeoperation, prior art designs have deposited a grid of black lines usingany suitable black material, such as carbon black, on the internalsurface of the viewing screen. Thereafter, the transparent conductivelayer and phosphor storage layer were deposited as described. This modeof graticule provision, while generally satisfactory, does involve theuse of a foreign blacking material as well as an additionalmanufacturing step thus adding to the initial cost of the tube.

With the above in mind, it is a primary object of the invention toprovide an internal graticule which will be visibly displayed andparticularly suited to the lowcontrast type tubes described.

It is another object of the invention to provide a plurality of voids inthe material distributed on the internal surface of the tube, such voidsappearing as black lines on the viewing screen when the tube isoperated. Specifically, the voids are positioned in relative arrangementdetermined by the graticule pattern desired.

It is a specific object of the invention to provide voids in theilluminescent phosphor layer which will effect a visible graticulepattern on the viewing screen during tube operation.

It is yet another object of the invention to provide voids of the typedescribed which may be used to expose segments of a transparentconductive layer below the phosphor layer and thus act as a path for thepassage of ejected secondary electrons to the conductive layer forcapture and disposition.

These and other objects of the invention will become apparent in thecourse of the following description and from an examination of therelated drawings wherein:

FIGURE 1 is a view of a segment of a cathode ray tube illustrating thegraticule of the disclosed invention as it would appear on the viewingscreen;

FIG. 2 is an enlarged view of the structure of FIG. 1 illustrating thepattern of phosphor disposition on the internal surface of the viewingscreen taken at circle 2 of FIG. 1;

FIG. 2(a) is a view similar to FIG. 2 of an alternate mode of phosphordisposition illustrating the phosphor layer as a plurality of segregatedisland segments; and

FIG. 3 is a sectional view taken along line 33 of FIG. 2.

Directing attention to FIGS. 1-3, numeral 10 indicates a segment of theglass viewing screen of a conventional cathode ray tube having a viewingsurface at 12. In conventional bistable cathode ray tubes a thintransparent coating 14, which is electrically conductive, is firstpositioned on the internal surface 16 of the viewing screen 10. Anysuitable transparent material may be used, tin oxide having been foundsatisfactory. In normal practice a thin coating of phosphor is thenplaced over the internal surface of the transparent film 14. Thephosphor provides the visible light pattern in that it will fluorescewhen struck by an appropriate electron beam.

In the construction of the phosphor coating, the present inventionteaches the preparation of a slurry of phosphor particles colloidallydisposed within a solution of an ultraviolet-sensitized polyvinylalcohol. The slurry is then placed over the surface of the transparentcoating 14 and dried. Thereafter, a mask is provided similar to the maskdisclosed in my referenced copending application and positioned over thedried slurry. The mask may be formed to define the graticule patterndesired. The arrangement is then exposed to an appropriate source ofultraviolet radiation, the mask intercepting the ultraviolet rays wheregraticule voids are desired. The exposed areas of the slurry become hardwhile the unexposed areas may be washed away after completion of theultraviolet radiation step. This type of phosphor printing technique isconventional and well known in the art and will not be further describedin detail.

After exposure and further processing, the internal surface 16 of thetube comprises first the transparent conductive coating 14 and uniformlydisposed and separated segments or sections of phosphor 18, 18. Thephosphor sections 18 define primary voids therebetween as at 20, 20,said voids 20 being arranged in perpendicular relationship to each otherto provide major graticule lines visible during tube operation, as shownby lines 21, 21 in FIG- URE 1. In a preferred embodiment of theinvention the voids 20 may be of an order of approximately .010 wide.Operating the tube with this construction, the voids 20, 20, will appearas the dark lines 21 on the viewing screen in the desired graticulepattern.

Additionally, segments 18 may define smaller voids therebetween asindicated by relatively narrow openings 22, 22, within each phosphorsegment 18. They may be provided by appropriate additions to the maskand using the procedures noted above.

The secondary voids 22 may be extremely narrow, e.g., .001" wide, so asto be effectively invisible during tube operation. Alternately, they maybe wide enough (.005 to be visible without the high definition of voids20. When thus visible, they would provide smaller visible increments tothe graticule pattern as shown by hair lines 25, 25 in FIG. 1.

FIG. 2(a) is a substantially enlarged view similar to FIG. 2 andillustrates a modification of the structure shown therein. Smalldiscrete independent segments of phosphor 18a are provided. In total,the segments may still define the major voids 20. Minor voids 2211 maybe provided between each segment 18a. The voids 220: may be dimensionedto be visible during tube operation as above described. Alternately, thevoids 22a may be dimensioned to be invisible yet serve as paths forcollection of secondary electrons by conductive layer 14. If desiredboth invisible and visible voids may be provided in the structuresdescribed.

In the operation of the embodiment shown in FIGS. 1-3, it will readilybe understood that as the viewing screen is bombarded by an appropriateelectron source, the phosphor segments 18 fluoresce and the intelligencepattern thereof will be visible at the surface 12. At the voids 20 and22, the fluorescing effect will be absent because of the lack ofphosphor coating in such voids. The voids, therefore, will appear asvisible black lines at the viewing screen 12 and thus offer the desiredvisible graticule pattern.

The phosphor segments 18 and 18a may be used as a storage target as iswell known in the art. Under writing electron bombardment the phosphorsegments emit secondary electrons and the voids 20, 22, and 22a serve asopenings or paths whereby the emitted secondary electrons may travel tothe conductive coating 14. Thus, a sparse or low-density phosphorpattern need not be used and the clarity and resulting sharpness of thedisplayed image importantly improved.

The invention thus provides a simple, easily manufactured structureparticularly suited to the provision of a visible internal graticule forthose cathode ray tubes which have inherent lowcontrast characteristics.The invention, however, conceivably may be applied to other type displaytubes.

These features and advantages of the invention are by way ofillustration only and the invention may be modified in many particularsall within the general scope thereof.

What is claimed is:

1. In a cathode ray tube,

the combination of a transparent image screen,

a continuous uninterrupted transparent conductive layer positioned onthe internal surface of the screen,

a plurality of illuminescent phosphor segments distributed over theinner surface of the conductive coating,

said segments defining therebetween primary voids having no phosphordistributed therein,

secondary voids defined by said segments, said sec ondary voids havingno phosphor distributed therein and being distributed over the screen inuniform patterned relationship to each other and to the primary voids,

said voids being arranged in generally perpendicular relation to eachother and of uniform pattern over the screen to define a visibledark-lined graticule pattern on the screen during tube operation andphosphor fluorescence,

the width of the secondary voids being less than the width of theprimary voids whereby the components of the dark-lined pattern due tothe primary voids are of a visibly darker intensity than the dark-linedpattern due to the secondary voids,

said voids providing travel paths for secondary electrons emitted fromsaid phosphor segments to said conductive coating.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 10/ 1943Switzerland.

4/1943 France.

ROBERT SEGAL, Primary Examiner.

